1. Field of the Invention
The present invention relates to an electronic apparatus and, more specifically, to an electronic apparatus having a function of communication using a fiber optic cable or an electric cable, which uses a detachable communication cable.
2. Description of the Background Art
Among digital video camera (digital VTRs with camera; digital video camera, hereinafter referred to as DVC) recording motion pictures, some have a function of transferring digital data at high speed to other electronic apparatuses, by connecting electronic apparatuses with each other by a cable, utilizing a standard such as IEEE1394.
In most cases, such electronic apparatuses are used as portable apparatuses. Therefore, generally, such an apparatus is used for recording pictures or the like while it is not connected to a cable, and communication with other apparatus is established by connecting a cable when communication becomes necessary.
An electric cable having a 4-pin or 6-pin terminal has been standardized as a communication medium in accordance with IEEE1394. As to the optical fiber, a standard specifying use of two optical fibers has been proposed. Further, mainly for portable apparatuses, study has been made for transferring signals in accordance with IEEE1394 standard over one optical fiber.
According to IEEE1394, when an electronic apparatus has a plurality of ports, it is necessary for the electronic apparatus to function as a repeater to relay a signal from one electronic apparatus to another electronic apparatus. Therefore, power supply to a physical layer circuit is adapted to be supplied constantly.
In an electronic apparatus not mainly used for communication, constant power supply to the physical layer circuit when the cable is not connected is unnecessary. Though IEEE1394 suggests possibility of considerable reduction of power consumption of a communication circuit when the communication cable is not connected, specific method thereof is not specified in the standard.
Further, a receptacle specified in IEEE1394 does not have any mechanism for detecting whether a plug is inserted to/removed from the receptacle. Therefore, it is necessary to detect voltage levels of signal lines in accordance with IEEE1394, to obtain information of connection between the plug and the receptacle from the result of analysis. This means that power must be supplied constantly to the communication circuit to keep the circuit in operation.
Here is the problem that even when the apparatus is fully disconnected from a communication circuit and the communication circuit is not in use, power consumption by the communication circuit portion cannot be made zero. In a portable apparatus such as a DVC, the communication circuit portion operates not only at the time of communication but also at the time of recording, for example, and hence power is consumed at the communication circuit portion which is essentially not in use. In such portable apparatus which are in most cases battery-operated, this leads to shorter discharge life of the battery, and the recordable time in recording operation is undesirably made shorter.
Generally, not only in DVCs but also in battery operated portable apparatuses, wasteful power consumption at the communication circuit portion not at the time of communication shortens discharge time of the battery, making it difficult to ensure long operation time of the apparatuses.
Therefore, reduction in power consumption of the electronic apparatus is an important problem.
As one technique related to lower power consumption of an electronic apparatus, Japanese Patent Laying-Open No. 7-57819 discloses a technique in which power supply of the electronic apparatus as a whole is shut off, when a cable is not connected to the electronic apparatus.
Though it is possible to control power supply to the overall electronic apparatus by the technique described in Japanese Patent Laying-Open No. 7-57819, it is not possible to reduce power consumption by the communication circuit portion only of the electronic apparatus, or to control power on port by port basis in accordance with IEEE1394, for example.
Japanese Patent Laying-Open No. 10-70508 discloses another related technique providing both spatial optical communication function and optical communication function through fiber optic cable, in which driving power for optical communication is increased to perform spatial optical communication when a fiber optic cable is not connected, and driving power for optical communication is reduced to perform optical communication through an optical fiber when the fiber optic cable is connected.
The technique described in Japanese Patent Laying-Open No. 10-70508 is applicable when spatial optical communication and optical communication through fiber optic cable are switched. The technique, however, cannot directly be applied to a DVC, for example, of which communication with other apparatus is established only through a communication cable.
In addition to the problem of power consumption, there is another problem of stabilizing operation when electronic apparatuses in operation are to be connected with each other by a communication cable.
Generally, when electronic apparatuses in operation are to be connected to each other by a communication cable, it is not guaranteed that the ground (reference potential) of an apparatus is at the same potential as the ground of the other apparatus to be connected, immediately before connection. Accordingly, when signal electrodes of the apparatuses contact with each other before the ground electrodes are connected to each other, it is possible that signal electrodes of the two apparatuses may contact with excessive potential difference therebetween. Therefore, a receiving device or a transmitting device may possibly be damaged.
FIG. 10 shows shapes of a plug and a receptacle in compliance with IEEE13344 standard.
Referring to FIG. 10, a receptacle 410 includes a power supply related electrode 415, and a signal electrode 417. Power supply related electrode 415 is positioned close to a tip end portion of receptacle 410, whereas signal electrode 417 is placed recessed therefrom. A plug 400 includes plug side electrodes 420 corresponding to respective electrodes of receptacle 410.
Therefore, when plug 400 is connected to receptacle 410, power supply related electrode 415 comes to be in contact with the corresponding plug side electrode 420 before signal electrode 417 comes into contact with the corresponding plug side electrode 420. Therefore, between the apparatuses, the ground (reference potential) and the power supply are first connected, and after the apparatuses are ready to have the signal lines connected to each other, the signal related electrode 417 comes to be in contact with the plug side electrode 420, establishing safe connection of the signal line. Accordingly, problems such as an unexpected application of excessive voltage to the receiving device or the transmitting device or malfunction caused by unexpected data input to a state transition circuit in accordance with IEEE1394 can be solved.
Generally, when electronic apparatuses in operation are to be connected with each other by a communication cable, unexpected data may possibly be input as a noise to the receiving side dependent on the order of connection of a plurality of signal lines, causing malfunction of a communication circuit.
In order to solve such a problem, a technique for preventing malfunction at the time of connection between the plug and the receptacle is described in Japanese Patent Laying-Open No. 2-53125.
FIG. 11 shows configurations of a plug and a receptor disclosed in Japanese Patent Laying-Open No. 2-53125.
Referring to FIG. 11, in a plug 500 and a receptacle 510, electrodes are arranged aligned in the direction vertical to the direction of insertion. At opposing ends of the plug and the receptacle, electrodes 512 and 514 for detecting connection and corresponding plug side electrodes 502 and 504 are provided respectively, separate from the electrodes for transmitting signals. By this configuration, it becomes possible to determine, when voltage levels of plug electrodes 502 and 504 do not match, that connection is now being established, and hence it becomes possible to interrupt operations of the electronic apparatuses and to prevent malfunction.
Development has been made to reduce area occupied by a receptacle of an apparatus by applying a miniature concentric plug (hereinafter also referred to as a mini plug) as an electric plug in accordance with IEEE1394 standard, for example, and providing an optical mini jack (OMJ) used commonly for optical and electric applications as a corresponding receptacle.
The structure of the OMJ will be described in detail later. In the OMJ, there is provided a terminal corresponding to an electric mini plug, and in addition, a photoreceptor circuit for processing an optical signal and a light emitting circuit (these circuits will be generally referred to as optical front-end circuit in the following) operable when a fiber optic plug having the same shape as the mini plug is inserted. Therefore, one receptacle can be commonly used to receive an optical plug and an electric plug. As a result, it becomes unnecessary to provide two receptacles for an optical signal and an electric signal, enabling reduction in size of the apparatus.
Further, study has been made to transfer signals in accordance with IEEE1394 standard over one optical fiber, on the premise that a small receptacle such as the OMJ is applied.
In such an electric mini plug and in the OMJ, electrodes are arranged aligned parallel to the direction of insertion, as will be described in detail later. Such arrangement of electrodes prevents application of the prior art shown in FIG. 11, and therefore there is a possibility that signal terminals may be in contact with each other before the ground terminals are connected, during the operation of insertion. Therefore, it is possible that signal electrodes of two apparatuses may be brought into contact with excessive potential difference therebetween. If a transmitting/receiving device having low breakdown voltage is used, such a device may be damaged.
There is still another problem. When an electric mini plug and an OMJ receptacle, for example, to be fitted in the mini plug are applied to the communication standard such as IEEE1394, it is the case that electrodes of the plug are brought into contact with electrodes other than the corresponding electrodes of the receptacle in the process of insertion, before the plug is fully inserted and connected to the corresponding electrodes of the receptacle, if the mini plug having such an electrode arrangement is inserted to the receptacle.
In the IEEE1394 standard, such an event in that plug electrodes are brought into contact with electrodes other than the corresponding electrodes of the receptacle when the plug is inserted is not considered. Therefore, when a mini plug represented by the OMJ is used, unexpected data may possibly be input, causing malfunction, as electrodes not corresponding to each other are brought into contact when the plug is inserted, affecting the communication circuit.
More specifically, though the plug and the receptacle having such shapes as shown in FIG. 11 solve the general problem of malfunction, the mini plug and the OMJ having such shapes in that electrodes are arranged parallel to the direction of insertion cannot solve these problems.
Further, in the plug and the receptacle defined by IEEE1394 shown in FIG. 10, positional relation between the power supply terminal and the signal terminal are adjusted to prevent the above described problems of malfunction or electric breakdown. The receptacle, however, occupies a large area on the surface of the apparatus. A receptacle considering common use with an electric cable, when an optical fiber is used, is not defined. Therefore, it is necessary to provide separate receptacles for optical signals and the electric signals. From these points, the plug and the receptacle defined by IEEE1394 shown in FIG. 10 are not suitable for application to a small portable apparatus.
An object of the present invention is to reduce power consumption of an electronic apparatus which communicates with other apparatus using a communication cable and capable of limited communication with the other apparatuses.
Another object of the present invention is to realize stable operation at the time of connection, in an electronic apparatus using a mini plug, which allows reduction in size and common use for optical and electric applications, and a fitting receptacle.
Briefly stated, the present invention provides an electronic apparatus to and from which a communication cable is attached and detached, including a detecting unit, a communication unit and a power control unit.
The detection unit detects state of connection of the communication cable. The communication unit communicates signals with the communication cable. The power control unit controls power supply to the communication unit, based on the result of detection by the detecting unit.
According to another aspect, the present invention provides an electronic apparatus to and from which a communication cable can be attached and detached, including a receptacle, a detecting unit, a communication unit and a switch unit.
The receptacle is provided to receive a plug of the communication cable inserted thereto. The detecting unit detects the state of insertion of the plug to the receptacle. The communication unit communicates signals with the communication cable. The switch unit is provided between the receptacle and the communication unit, and operates based on the result of detection by the detecting unit.
Therefore, an advantage of the present invention is that, in an electronic apparatus having the function of attaching/detaching a communication cable, power supply to the communication unit is stopped and power consumption is reduced except in a communication period in which the communication cable is connected. Therefore, the time of battery discharge of a portable apparatus can be made longer, and the operation time of the apparatus can be made longer.
Further, connection between the receptacle and the communication unit is established after insertion of the plug into the receptacle is detected. Therefore, electric breakdown of the receiving device or the transmitting device at the time of inserting the plug can be prevented. Further, malfunction at the communication unit caused by undesirable contact with other terminal in the course of inserting the plug can be prevented.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.